Because of present day fuel shortages and demands, the need for fuel conservation and economy with respect to the operation of motor driven vehicles is of prime importance. One way to satisfy this need is to develop smaller engines to do the work of larger engines which have previously been used. To be efficient, an internal combustion engine, gasoline or diesel, must be operated within a certain range of speeds (rpm settings). To accomplish this, more and more closely spaced gear changes must be provided while giving ease of operation so that such changes will be accepted by the driving public.
Overdrive transmission mechanisms have been used in the past to provide fuel and other economies. However, the principal fault with such a mechanism has been in the control of it inasmuch as a vehicle driver, to operate such a mechanism, had to operate the vehicle at a full power condition, let the vehicle slow to a relatively slow speed, or switch the vehicle ignition system on and off to get the transmission out of the overdrive. Because of these disadvantages of operation, only minimal control of the overdrive was possible and this fact contributed to the decline in acceptance by the driving public of conventional transmission systems.